1. Field of the Invention
This invention relates to small down-flow furnaces whose combustion gases are vented upward through a broad, radiator member curving inward to a flue.
2. Related Art
Down-flow furnaces, in which room air is delivered downward over heat-exchanger surfaces, have been used for many years, especially in mobile homes which utilize the balanced draft afforded by concentric flues. The room air is conventionally directed over a combustion chamber mounted in the lower part of a furnace cabinet, which serves as the primary heat exchanger. Heated air is discharged through a system of floor ducts. See for example U.S. Pat. Nos. 3,171,400, and 3,601,116. As shown in those patents, it is conventional to permit the upflow of combustion gases to the flue through a broad radiator member curved around the centrifugal blower; this radiator member serves as the final heat exchanger. The gas from the upper part of the combustion chamber is ducted to the radiator member by a short cylindrical flue connector.
In order to achieve much greater efficiency in the utilization of the fuel, much more complex furnaces have been designed, such as shown in U.S. Pat. No. 4,621,686, issued Nov. 11, 1986; these extract even the latent heat of condensation of combustion gases. That patent shows a finned heat exchanger positioned on a slant beneath the outlet of a centrifugal blower. A suction fan draws the gases downward, through the heat exchanger, removes the condensate, and expels the combustion. Such high-efficiency furnaces are costly to manufacture and have not proved to be popular.